1. Field of the Invention
This invention relates to control device and method for controlling a fuel injection timing for use in an internal combustion engine, and particularly to control device and method for controlling a fuel injection timing to a proper timing irrespective of variations of engine driving conditions, such as variation of viscosity of fuel, by detecting a lift timing of a needle valve for a fuel injection nozzle and determining a target lift timing.
2. Description of Related Art
In an internal combustion engine such as a diesel engine, fuel is forcedly fed from a fuel injection pump to a fuel injection nozzle at a controlled timing within a rotational period of an engine while pressurized by the fuel injection pump. When the fuel is fed into the fuel injection nozzle, a needle valve which is urged by a spring is pushed (lifted) up by the pressure of the fuel itself to open a fuel injection port, whereby the fuel is injected through the fuel injection port into a combustion chamber.
Such a fuel injection mechanism is generally provided with a fuel injecting timing control device for detecting a lift timing of a needle valve and performing a feedback control so that the detected lift timing is coincident with a target lift timing which is beforehand determined, as disclosed in Japanese Laid-open Patent Application No. 4-17754.
The conventional fuel injection Liming control device as described above is equipped with a sensor for detecting the lift motion of the needle valve, and a start timing of the lift of the needle valve, that is, a start timing of the fuel injection is detected on the basis of an output signal from the sensor. Further, the fuel injection timing control device is equipped with a map containing various fuel injection timings which are optimally determined in accordance with various loads (injection amounts) and rotating numbers of the engine in advance. In a driving condition, a fuel injection timing which is optimal to the driving condition (load, rotating number) is read out from the map, and the read-out timing is used as a target fuel injection timing. The timing of the forced fuel feeding of the fuel injection pump is controlled so that the detected lift start timing of the needle valve is coincident with the target fuel injection timing.
In the conventional fuel injection control device as described above, if any engine driving condition, particularly viscosity of fuel, is varied, excess and deficiency would occur in a spark advance for the fuel injection timing, resulting in aggravation of noises, aggravation of emission, failure of ignition, etc.
FIGS. 1A, 1B and 1C are graphs each showing the waveform of an output signal of the needle valve lift sensor, that is, variation of an lift amount of the needle valve under various conditions. Specifically, FIG. 1A shows the waveform of the output signal under the condition of low speed and low load, FIG. 1B shows the waveform of the output signal under the condition of intermediate speed and intermediate load, and FIG. 1C shows the waveform of the output signal under the condition of high speed and high load. In the figures, waveforms as indicated by a solid line and a dotted line are obtained in case of using fuels having different viscosity. Further, a point A represents a start timing of the needle valve, and it is a timing which is a control target by the conventional control device. On the other hand, a point B represents a timing when an accumulation amount of fuel in a combustion chamber reaches an amount which is required for ignition, that is, an amount at which the fuel can be ignited (hereinafter referred to as "ignition point"). Actually, the phase of the point B, not the point A, greatly effects emission, failure of ignition and other phenomena.
In addition, particularly when a phase distance (difference) between the point A and the point B is greatly varied in accordance with viscosity of fuel as shown in FIG. 1B (intermediate speed and intermediate load), it is impossible to control the point B to a proper timing at all times irrespective of viscosity of fuel.
In view of the foregoing, in order to perform a proper fuel injection timing control, the point B (not the point A) should be originally used as a control target. However, as described above, in the conventional fuel injection timing control device, the point A is used as a control target, and thus there are the disadvantages as described above.